I built a few hitch receivers on pop-up campers. They extended under the trailer and attached to the bumper and two cross members that I also reinforced. Brother-in-law had a welding shop install a receiver on the bumper of his pop-up. All they did was butt weld a stub on the face of the bumper. I told him that was no good, he said it was a professional welder who said it was fine. When it broke off on I-84 and the bikes were dragging in the road behind the trailer I just had to say "I told you so". Then he asked me to fix it, which I did.

A butt weld with a cantilevered load sounds like an accident waiting to happen. The 2"x3" channel that holds our extension continues to the front of the trailer. It's welded to the side of the original thin wall box tubing. It has an aluminum pickup bed box on it, then the bike rack. The new axel and larger tires which adds ground clearance are rated at 3,500#'s. We also tow a small motorcycle trailer behind the Burro (not legal in all states). The tongue was extended as well to add stability.

Tried many ideas for a bike rack, but what always bugs me is safety, to make sure the bike would be well-attached at the back (and not flying in the car behind), and also having to remove it at night (having heard many stories of stolen bikes).
So, I looked for a not-too-expensive foldable bike, and received last week the Schwinn 20-inch Loop https://goo.gl/IWdMVi for under $250 (shipping included).
Easy to setup, solid, lifetime warranty, and has lots of good reviews.
Comes with a carry-bag. So, now thinking on how to mount it on the roof.
And fun to ride

We pull our 16' Casita, and travel with the mountain bikes inside the Chevy trailblazer and canoe on top. That way we can leave camp, drive to a bike trail and have clean bikes safely with us at all times. No worry about weight, sway, or theft.